Device comprising a blood pressure sensor and a method for controlling the device

ABSTRACT

There is provided a device comprising a blood pressure sensor for sensing blood pressure and a method for controlling the device. An angle of the device with respect to the direction of gravity is determined (202) and a location of one or more features of the user holding the device is identified (204). A height of the blood pressure sensor relative to a heart level of the user is determined based on the determined angle of the device with respect to the direction of gravity and the identified location of the one or more features of the user (206). The device is controlled based on the determined height of the blood pressure sensor relative to the heart level of the user (208).

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§ 371 of International Application No. PCT/EP2017/077944, filed on 1Nov. 2017, which claims the benefit of European Patent Application No.16197456.3, filed on 7 Nov. 2016. These applications are herebyincorporated by reference herein.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a device comprising a blood pressure sensor anda method for controlling the device.

BACKGROUND TO THE INVENTION

Blood pressure (BP), or more precisely, arterial blood pressure, is thepressure exerted by circulating blood on arterial vessel walls. It isone of the key vital signs to establish the well-being of a subject.Since blood pressure is dynamic and changes periodically due the pumpingaction of the heart, blood pressure is typically described by systolicblood pressure (SBP), which is the maximal blood pressure during theheart cycle, diastolic blood pressure (DBP), which is the minimal bloodpressure during the heart cycle, and mean arterial blood pressure (MAP),which is the average blood pressure during the heart cycle.

In the past, non-invasive blood pressure measurements were typicallyperformed by using a sphygmomanometer, which uses a column of mercury toreflect blood pressure. Nowadays, devices for blood pressuremeasurements are often cuff-based. The measurement procedure is oftenautomated, especially when the device is not intended for theprofessional caregiver. The most commonly used and clinically acceptedautomatic blood pressure measurement uses the oscillometric bloodpressure measurement principle. This measurement principle generallyconsists of placing a cuff around a limb (usually the upper arm) of asubject and inflating it rapidly. After this, cuff pressure is graduallyor stepwise decreased, during which the arterial volume oscillationscause small pressure oscillations in the cuff. The diastolic bloodpressure (DBP) and the systolic blood pressure (SBP) are estimated fromthese cuff pressure dependent amplitudes of the cuff pressure or volumeoscillations using heuristic algorithms. The mean arterial pressure(MAP) is then usually calculated from the diastolic blood pressure (DBP)and the systolic blood pressure (SBP) using a heuristic formula or byassuming it is equal to the pressure at maximum oscillations. Instead ofusing the pressure oscillations during deflation, the oscillations canalso be measured during inflation.

Other blood pressure measurement techniques have been developed that donot require an external cuff. This has been possible due to the rapiddevelopments in the mobile device industry (particularly, the smartphoneindustry), which allow a user to have a plurality of high qualitysensors in a single device. For example, a user of a smartphone is nowable to perform an oscillometric blood pressure measurement usingsensors in a smartphone. WO 2016/096919 A1 discloses an example of apersonal hand-held monitor for the measurement of a subject's bloodpressure, where a pressure sensor is embedded in the monitor to providean electrical signal indicative of the pressure applied to it by a bodypart of the subject such that the flow of blood in the body part can bedetected and a blood pressure measurement provided.

However, while these recent techniques that eliminate the need for acuff are more convenient for the user, the blood pressure measurementsacquired by these techniques can suffer from inaccuracies due to theeffects of hydrostatic pressure. In order to avoid the effects ofhydrostatic pressure, blood pressure measurements need to be taken at orclose to the level of the heart of the user since any height differencebetween the blood pressure measurement location and the heart level willresult in a hydrostatic offset. If the blood pressure measurements aretaken above the level of the heart, the measurement results will be toolow, whereas if the blood pressure measurements are taken below thelevel of the heart, the measurement results will be too high. For everycentimetre difference between the blood pressure measurement locationand the heart level, 0.73 mmHg is erroneously introduced to the bloodpressure measurement. Thus, if the blood pressure measurement is takenfrom a finger while the arm is in a relaxed (i.e. in a hangingposition), a height difference of 50 cm can easily be made, which canresult in hydrostatic offsets of approximately 37 mmHg.

As an untrained user usually takes the blood pressure measurement in thehome environment, it is often the case that the blood pressuremeasurements are taken at heights that are significantly different tothe heart level of the user, which can introduce large errors in theblood pressure measurements. This is especially relevant for cuff-lessdevices, as cuff-less devices do not restrict the counter pressure to beapplied at heart level, whereas cuff-based measurements on an upper armwill always be relatively close to the heart level. Therefore, a deviceaimed at minimising, preventing or eliminating hydrostatic effects toprovide more accurate blood pressure measurements is required.

There is thus a need for an improved device comprising a blood pressuresensor and an improved method for controlling the device.

SUMMARY OF THE INVENTION

As noted above, the limitation with existing approaches is that errorscan be introduced into blood pressure measurements due to hydrostaticeffects. It would thus be valuable to have a device comprising a bloodpressure sensor and a method for controlling the device in a manner thatovercomes these existing problems.

Therefore, according to a first aspect of the invention, there isprovided a method for controlling a device comprising a blood pressuresensor for sensing blood pressure. The method comprises determining anangle of the device with respect to the direction of gravity,identifying a location of one or more features of the user holding thedevice, determining a height of the blood pressure sensor relative to aheart level of the user based on the determined angle of the device withrespect to the direction of gravity and the identified location of theone or more features of the user, and controlling the device based onthe determined height of the blood pressure sensor relative to the heartlevel of the user.

In some embodiments, the one or more features of the user holding thedevice may comprise one or more anatomical features of the user holdingthe device. In some embodiments, the location of the one or morefeatures may be identified in a displayed image of the user. In someembodiments, the location of the one or more features may be identifiedrelative to a displayed predefined location range. In these embodiments,the height of the blood pressure sensor relative to a heart level of theuser may be determined based on the determined angle of the device withrespect to the direction of gravity and the identified location of theone or more features of the user in the image relative to the predefinedlocation range.

In some embodiments, the height of the blood pressure sensor may bedetermined to be different to the heart level of the user where thedetermined angle of the device with respect to the direction of gravityis outside a predefined angle range and/or the identified location ofthe one or more features of the user is outside a predefined locationrange.

In some embodiments, the height of the blood pressure sensor may bedetermined to be at the heart level of the user where the determinedangle of the device with respect to the direction of gravity is within apredefined angle range and/or the identified location of the one or morefeatures of the user is within a predefined location range.

In some embodiments, controlling the device based on the determinedheight of the blood pressure sensor may comprise controlling the deviceto output to the user one or more of the determined angle of the devicewith respect to the direction of gravity and the identified location ofthe one or more features of the user when the height of the bloodpressure sensor is determined to be different to the heart level of theuser.

In some embodiments, controlling the device based on the determinedheight of the blood pressure sensor may comprise controlling the deviceto output to the user an instruction to adjust one or more of the angleof the device with respect to the direction of gravity and the locationof the one or more features of the user when the height of the bloodpressure sensor is determined to be different to the heart level of theuser.

In some embodiments, controlling the device based on the determinedheight of the blood pressure sensor may comprise controlling the deviceto output to the user an error notification when the height of the bloodpressure sensor is determined to be different to the heart level of theuser.

In some embodiments, controlling the device based on the determinedheight of the blood pressure sensor may comprise controlling the bloodpressure sensor to acquire a blood pressure measurement from the userwhen the height of the blood pressure sensor is determined to be at theheart level of the user.

In some embodiments, controlling the device based on the determinedheight of the blood pressure sensor may comprise controlling the bloodpressure sensor to acquire a blood pressure measurement from the userwhen the height of the blood pressure sensor is determined to bedifferent to the heart level of the user, and adjusting the acquiredblood pressure measurement based on the difference between the height ofthe blood pressure sensor and the heart level of the user.

In some embodiments, the one or more features of the user may compriseany one or more of one or both eyes of the user, the mouth of the user,the nose of the user, and the facial outline of the user.

According to a second aspect of the invention, there is provided acomputer program product comprising a computer readable medium, thecomputer readable medium having computer readable code embodied therein,the computer readable code being configured such that, on execution by asuitable computer or processor, the computer or processor is caused toperform the method or the methods described above.

According to a third aspect of the invention, there is provided a devicecomprising a blood pressure sensor for acquiring a blood pressuremeasurement from a user holding the device and a control unit. Thecontrol unit is configured to determine an angle of the device withrespect to the direction of gravity, identify a location of one or morefeatures of the user holding the device, determine a height of the bloodpressure sensor relative to a heart level of the user based on thedetermined angle of the device with respect to the direction of gravityand the identified location of the one or more features of the user, andcontrol the device based on the determined height of the blood pressuresensor relative to the heart level of the user.

In some embodiments, the one or more features of the user holding thedevice may comprise one or more anatomical features of the user holdingthe device. In some embodiments, the location of the one or morefeatures may be identified in a displayed image of the user. In someembodiments, the location of the one or more features may be identifiedrelative to a displayed predefined location range. In these embodiments,the height of the blood pressure sensor relative to a heart level of theuser may be determined based on the determined angle of the device withrespect to the direction of gravity and the identified location of theone or more features of the user in the image relative to the predefinedlocation range.

In some embodiments, the device may further comprise an angular sensorand the control unit may be configured to control the angular sensor todetermine the angle of the device with respect to the direction ofgravity.

In some embodiments, the device may further comprise a camera and thecontrol unit may be configured to control the camera to identify thelocation of the one or more features of the user when the user is, atleast partially, in the field of view of the camera.

In some embodiments, the device may further comprise a user interfaceand, when the height of the blood pressure sensor is determined to bedifferent to the heart level of the user, the control unit may beconfigured to control the user interface to output to the user any oneor more of the determined angle of the device with respect to thedirection of gravity, the identified location of the one or morefeatures of the user, an instruction to adjust any one or more of theangle of the device with respect to the direction of gravity, thelocation of the one or more features of the user, and an angle of thebody of the user, and an error notification.

In some embodiments, the blood pressure sensor may comprise any one ormore of a volume sensor and a pressure sensor.

According to the aspects and embodiments described above, thelimitations of existing techniques are addressed. In particular,according to the above-described aspects and embodiments, hydrostaticeffects in blood pressure measurements can be prevented, reduced, oreliminated. In this way, more accurate blood pressure measurements canbe acquired by way of a simple yet effective method.

There is thus provided an improved device comprising a blood pressuresensor and an improved method for controlling the device, whichovercomes the existing problems.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show more clearlyhow it may be carried into effect, reference will now be made, by way ofexample only, to the accompanying drawings, in which:

FIG. 1 is a block diagram of a device according to an embodiment;

FIG. 2 is a flow chart illustrating a method according to an embodiment;and

FIG. 3 is an illustration of a device in use according to an embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As noted above, the invention provides an improved device comprising ablood pressure sensor and an improved method for controlling the device,which overcomes the existing problems.

FIG. 1 shows a block diagram of a device 100 according to an embodiment.In some embodiments, the device 100 may be a device dedicated for bloodpressure measurements. In other words, the device 100 can be a bloodpressure measurement device. Alternatively, in some embodiments, inaddition to blood pressure measurements, the device 100 may also beintended for other purposes or uses. The device 100 may be a mobiledevice. For example, the device 100 can be a smart phone, a tablet, asmart watch, or any other mobile device.

As illustrated in FIG. 1, the device 100 comprises a blood pressuresensor 102 for sensing blood pressure (or for acquiring a blood pressuremeasurement) from a user holding the device 100. In operation, toacquire a blood pressure measurement, the user holds the device 100 (forexample, in front of them) such that a part of the body of the user (forexample, a finger or thumb of the user) is positioned at or contactswith the blood pressure sensor 102. The part of the body of the user maybe in direct contact with the blood pressure sensor 102 or indirectcontact with the blood pressure sensor 102.

In some embodiments, the user may be instructed (such as via a userinterface of the device 100) to increase the pressure applied by thepart of the body that is in contact with the blood pressure sensor 102.For example, the user may be instructed to increase the pressure appliedby the part of the body that is in contact with the blood pressuresensor 102 by a pressure profile generated over time, which the user canfollow by increasing the applied pressure. Examples of a pressureprofile include, but are not limited to, a numerical target thatincreases over time, a line or bar that becomes increasingly full aspressure is increased with target pressures at one or more points intime, or any other pressure profile.

The blood pressure sensor 102 of the device 100 can comprise any sensor,or any combination or sensors, suitable to acquire a blood pressuremeasurement from a user holding the device 100. The blood pressuremeasurement may, for example, be acquired from arterial oscillationsdetected by the blood pressure sensor 102. An increase in pressureapplied by the part of the body of the user that is in contact with theblood pressure sensor 102 can result in arterial oscillations, which canthen be detected by the blood pressure sensor 102. The blood pressuresensor 102 can comprise any one or more of a volume sensor, a pressuresensor, or any other sensor, or any combination of sensors, suitable toacquire a blood pressure measurement from a user holding the device 100.

A volume sensor can comprise any volume sensor that is suitable todetect arterial oscillations (specifically, volumetric oscillations)from the part of the body of the user that is positioned at the volumesensor of the device 100, which can be used to acquire a blood pressuremeasurement. Examples of a volume sensor include, but are not limitedto, a light sensor, or any other volume sensor, or any combination ofvolume sensors. A light sensor can comprise any light sensor that issuitable to detect light indicative of volumetric oscillations from auser holding the device 100, which can be used to acquire a bloodpressure measurement. For example, a light sensor can comprise an imagesensor, a plethysmography (PG) sensor (such as a photoplethysmography(PPG) sensor), or any other light sensor, or any combination of lightsensors.

An image sensor can comprise any image sensor that is suitable toacquire an image from a user holding the device 100, which can be usedto acquire a blood pressure measurement. Examples of an image sensorinclude, but are not limited to, a camera, a video recording device, orany other image sensor, or any combination of image sensors. The imagemay comprise a single image frame or a plurality of image frames. Forexample, the plurality of image frames may be in the form of a “live”,instantaneous, or real-time (or near real-time) series of image framesor video of the user holding the device. The image acquired by the imagesensor can be indicative of arterial oscillations (specifically,volumetric oscillations) in the part of the body of the user that is inthe image. In some embodiments, for example, the image acquired by theimage sensor may be averaged to acquire a volume measurement.

A photoplethysmography (PPG) sensor can comprise anyphotoplethysmography sensor suitable to acquire photoplethysmographicdata from the user holding the device 100, which can be used to acquirea blood pressure measurement. Examples of a photoplethysmography sensorinclude, but are not limited to, a reflective PPG sensor, a transmissivePPG sensor, or any other photoplethysmography sensor, or any combinationof photoplethysmography sensors. The photoplethysmographic data acquiredby the photoplethysmography sensor can be indicative of arterialoscillations (specifically, volumetric oscillations) in the part of thebody of the user that is positioned at the photoplethysmography sensorof the device 100.

In some embodiments, a light sensor (such as a PPG sensor) can comprisea light source (for example, a white light emitting diode LED, a singlewavelength light such as a light emitting in the red region, or anyother light source) and an associated light detector. For example, insome embodiments, a light source may be operable to project light onto apart of the body of the user holding the device 100 and the lightdetector may be operable to detect transmitted or reflected light. Thelight detected by the light detector can be indicative of arterialoscillations (specifically, volumetric oscillations) in the part of thebody of the user onto which light is projected.

A pressure sensor can comprise any pressure sensor that is suitable toacquire the applied pressure and the arterial oscillations(specifically, pressure oscillations) from a part of the body of theuser that is in direct or indirect contact with the pressure sensor ofthe device 100, which can be used to acquire a blood pressuremeasurement. Examples of a pressure sensor include, but are not limitedto, a pressure sensitive display, a pressure sensitive element below adisplay (such as a foil, thin-film flexible printed circuit, orsimilar), a force sensor where a contact area of the force sensor with apart of the body of the user is known (for example, assumed to beconstant) or can be measured, or any other pressure sensor, or anycombination of pressure sensors. The pressure oscillations can bedetermined from the force detected by a force sensor where the contactarea is known or measured since pressure is equal to the force per unitarea. In some embodiments, a pressure sensor can comprise multiple forcesensors integrated over an area.

A force sensor can comprise any force sensor suitable to detect a forceapplied by the user holding the device 100, which can be used to acquirea blood pressure measurement. Examples of a force sensor include, butare not limited to, a force sensitive display, a force sensitive elementbelow a display (such as a foil, thin-film flexible printed circuit, orsimilar), a strain gauge, a load cell (for example, a structurecomprising multiple strain gauges, or any other force sensor, or anycombination of force sensors.

Although examples have been provided for the blood pressure sensor 102,it will be understood that any other blood pressure sensor, or anycombination of blood pressure sensors, suitable to acquire a bloodpressure measurement from the user can be used.

As illustrated in FIG. 1, the device 100 also comprises a control unit104. The control unit 104 controls the operation of the device 100 andcan implement the method describe herein. The control unit 104 cancomprise one or more processors, processing units, multi-core processorsor modules that are configured or programmed to control the device 100in the manner described herein. In particular implementations, thecontrol unit 104 can comprise a plurality of software and/or hardwaremodules that are each configured to perform, or are for performing,individual or multiple steps of the method according to embodiments ofthe invention.

Briefly, the control unit 104 is configured to determine an angle of thedevice with respect to the direction of gravity, identify a location ofone or more features of the user holding the device, determine a heightof the blood pressure sensor relative to a heart level of the user basedon the determined angle of the device with respect to the direction ofgravity and the identified location of the one or more features of theuser, and control the device based on the determined height of the bloodpressure sensor relative to the heart level of the user.

In some embodiments, as illustrated in FIG. 1, the device 100 canfurther comprise an angular sensor 106. Examples of an angular sensorinclude, but are not limited to, an accelerometer or gravitationalsensor (such as a single-axis accelerometer, a dual-axis accelerometer,or a three-axis accelerometer), a gyroscope, a tilt-sensor, or any otherangular sensor, or any combination of angular sensors. The angularsensor 106 can be for use in determining the angle of the device withrespect to the direction of gravity. For example, in embodiments wherethe device 100 comprises an angular sensor 106, the control unit 104 canbe configured to control the angular sensor 106 to determine the angleof the device with respect to the direction of gravity.

In some embodiments, as illustrated in FIG. 1, the device 100 canfurther comprise a camera 108. The camera 108 can be for use inidentifying the location of the one or more features of the user whenthe user is, at least partially, in the field of view of the camera 108.For example, the control unit 104 can be configured to control thecamera 108 to identify the location of the one or more features of theuser when the user is, at least partially, in the field of view of thecamera 108. The camera 108 can be any camera that is directed at theuser. Thus, alternatively or in addition to the device comprising acamera 108, a camera 108 may be external to (i.e. separate to or remotefrom) the device 100.

In some embodiments, as illustrated in FIG. 1, the device 100 canfurther comprise a user interface 110. Alternatively or in addition, auser interface 110 may be external to (i.e. separate to or remote from)the device 100. A user interface 100 can be for use in providing a userof the device 100 with information, data, signals, or measurementsresulting from the method according to the invention. For example, thecontrol unit 104 can be configured to control a user interface 110 toprovide (for example, render, output, or display) information, data,signals, or measurements resulting from the method to the user of thedevice 100.

In some embodiments, the control unit 104 may be configured to control auser interface 110 to display an image of the user. As mentionedearlier, the image may comprise a single image frame or a plurality ofimage frames. For example, the control unit 104 may be configured tocontrol the user interface 110 to display a “live”, instantaneous, orreal-time (or near real-time) series of image frames or video of theuser holding the device 100. The control unit 104 may also be configuredto control the user interface 110 to display a predefined location rangefor the one or more features of the user. For example, the predefinedlocation range may be displayed over or through the image of the user.In some embodiments, the image of the user and the predefined locationrange may be displayed on the device 100 comprising the blood pressuresensor 102. Alternatively, in other embodiments, the image of the userand the predefined location range may be displayed on a device that is adifferent device to the device 100 that comprises the blood pressuresensor 102. For example, the device on which the image of the user andthe predefined location range are displayed may be external to (i.e.separate to or remote from) the device 100 comprising the blood pressuresensor 102.

In some embodiments, for example, the control unit 104 can be configuredto control a user interface 110 to provide (for example, render, output,or display) to the user one or more blood pressure measurements acquiredby the blood pressure sensor 102 of the device 100. Alternatively or inaddition, in some embodiments, when the control unit 104 of the device100 determines that the height of the blood pressure sensor 102 isdifferent to the heart level of the user, the control unit 104 can beconfigured to control a user interface 110 to provide (for example,render, output, or display) to the user any one or more of thedetermined angle of the device with respect to the direction of gravity,the identified location of the one or more features of the user, aninstruction to adjust one or more of the angle of the device withrespect to the direction of gravity and the location of the one or morefeatures of the user, an error notification, or any other informationresulting from the method described herein.

Alternatively or in addition, a user interface 110 may be configured toreceive a user input. In other words, a user interface 110 may allow auser of the device 100 to manually enter instructions, data, orinformation. The control unit 104 may be configured to acquire a userinput from the user interface 110.

A user interface 110 may be any user interface that enables rendering(or output or display) of information, data, signals, or measurements toa user of the device 100. Alternatively or in addition, a user interface110 may be any user interface that enables a user of the device 100 toprovide a user input, interact with and/or control the device 100. Forexample, a user interface 110 may comprise one or more switches, one ormore buttons, a keypad, a keyboard, a touch screen or an application(for example, on a smartphone, tablet, or similar), a display screen, agraphical user interface GUI or any other visual rendering component,one or more speakers, one or more microphones or any other audiocomponent, one or more lights, a component for providing tactilefeedback (such as a vibration function), or any other user interfacecomponent, or combination of user interface components.

Although not illustrated in FIG. 1, in some embodiments, the device 100may also comprise a memory configured to store program code that can beexecuted by the control unit 104 to perform the method described herein.The memory can be used to store information, data, signals andmeasurements acquired or made by the control unit 104 of the device 100.For example, the memory may be used to store blood pressure measurementsacquired by the blood pressure sensor 102 from the user of the device100.

Although not illustrated in FIG. 1, in some embodiments, the device 100may also comprise a communications interface for enabling the device 100to communicate with any sensors, interfaces, units, memories, devices orany other components that are internal or external to the device 100.The communications interface may communicate with any sensors,interfaces, units, memories, devices or any other components wirelesslyor via a wired connection. For example, in an embodiment where thecamera 108 is external to the device 100, the communications interfacemay communicate with the external camera 108 wirelessly or via a wiredconnection. Similarly, in an embodiment where a user interface 110 isexternal to the device 100, the communications interface may communicatewith the external user interface wirelessly or via a wired connection.

Thus, it will be appreciated that FIG. 1 only shows the componentsrequired to illustrate this aspect of the invention, and in a practicalimplementation the device 100 may comprise additional components tothose shown. For example, the device 100 may comprise a battery or otherpower supply for powering the device 100 or means for connecting thedevice 100 to a mains power supply.

FIG. 2 illustrates a method 200 for controlling the device 100comprising the blood pressure sensor 102. The illustrated method 200 cangenerally be performed by or under the control of the control unit 104of the device 100.

As mentioned previously, in operation, the user holds the device 100(for example, in front of them) such that a part of the body of the user(for example, a finger or thumb of the user) is positioned at orcontacts with the blood pressure sensor 102. In some embodiments,although not illustrated, the position of the part of the body of theuser on the device may be detected to ensure that the user is holdingthe device 100 correctly. For example, where the blood pressure sensor102 comprises a camera and a display (such as a force or pressuresensitive display) of the device 100, the user may place a finger (suchas an index finger) of a hand in front of the camera and a thumb of thehand on the display for the blood pressure measurement. The position ofthe thumb on the display can be measured and the camera can be used todetect the position of the finger to ensure that the user is holding thedevice 100 correctly. Alternatively or in addition, in some embodiments,the blood pressure sensor 102 may be located at one or more fixed pointson the device 100, which can be indicated to the user. For the purposeof the method disclosed herein, it may be assumed that the device 100 isheld approximately or exactly perpendicular to the body of the user.

With reference to FIG. 2, at block 202, an angle of the device 100 isdetermined with respect to the direction of gravity (or compared to theground level or earth). For example, as mentioned earlier, the controlunit 104 can be configured to control an angular sensor 106 of thedevice 100 to determine the angle of the device with respect to thedirection of gravity. In some embodiments, the angle of the body of theuser may be inferred from the angle of the device 100 with respect tothe direction of gravity.

As an angular sensor can measure gravitational force, the gravitationalforce component on the angular sensor can be used to determine the angleof the device 100 with respect to gravity. As mentioned earlier, theangular sensor can comprise an accelerometer (such as a single-axisaccelerometer, a dual-axis accelerometer, a three-axis accelerometer), agyroscope, a tilt-sensor, or similar and thus the angle of the device100 with respect to gravity can be determined in any of the standardways in respect of these angular sensors. For example, as is known, theacceleration due to gravity can be measured and related back to thereference frame of the device 100 to determine the angle of the device100 with respect to gravity.

At block 204, a location of one or more features (or landmarks) of theuser holding the device 100 are identified. For example, as mentionedearlier, the control unit 104 can be configured to control a camera 108of the device 100 to identify the location of the one or more featuresof the user when the user is (at least partially) in the field of viewof the camera 108. The one or more features of the user can comprise oneor more anatomical (e.g. physical) features of the user. In someembodiments, the one or more features of the user may comprise one ormore features of the torso (or upper torso) of the user, such as one ormore shoulders of the user, or any other features of the torso of theuser, or any combination of features of the torso of the user.Alternatively or in addition, in some embodiments, the one or morefeatures of the user may comprise the neck of the user. Alternatively orin addition, in some embodiments, the one or more features of the usermay comprise one or more facial features of the user, for example, anyone or more of the facial outline of the user, one or both eyes of theuser, the nose of the user, the mouth of the user, or any other facialfeatures of the user, or any combination of facial features of the user.Although examples have been provided for the one or more features of theuser, the person skilled in the art will be aware of other features ofthe user, or any combination of features of the user, that may be used.

In some embodiments, the method may further comprise determining thedistance of the device 100 with respect to the body based on the size,location, or both the size and location, of the one or more features.The distance may, for example, be determined as a horizontal distance.The distance can be indicative of the amount an arm of the user isstretched while holding the device 100 and can be used to improve themeasurement of height of the device relative to the heart level. Thedistance may, for example, be determined based on the apparent size ofthe one or more features identified by the camera 108. For example, thelarger a feature appears, the closer the feature is to the camera 108(which can be indicative of a bent arm) and, similarly, the smaller afeature appears, the farther the feature is from the camera 108 (whichcan be indicative of a straight arm).

At block 206, a height of the blood pressure sensor 102 relative to aheart level of the user is determined based on the determined angle ofthe device 100 with respect to the direction of gravity and theidentified location of the one or more features of the user.

In some embodiments, the method comprises determining whether thedetermined angle of the device 100 with respect to the direction ofgravity is within (or outside) a predefined angle range. In other words,it may be determined whether the determined angle of the device 100 withrespect to the direction of gravity is between (or falls outside) aminimum threshold value for the angle and a maximum threshold value forthe angle. The predefined angle range (or minimum and maximum thresholdvalues for the angle) can be set to indicate that the device 100 is heldupright or substantially upright. In one example, the predefined anglerange is between −30 degrees and +30 degrees. However, it will beunderstood that other predefined angles may be used instead. Similarly,in some embodiments, the method may further comprise determining whetherthe identified location of the one or more features of the user iswithin (or outside) a predefined location range. For example, thepredefined location range may be a predefined location range on adisplay of the device 100 comprising the blood pressure sensor 102 oranother device. The predefined location range on the display may bedefined by one or more lines or shapes.

In these embodiments, the height of the blood pressure sensor 102 may bedetermined to be different to the heart level of the user where thedetermined angle of the device with respect to the direction of gravityis outside a predefined angle range, the identified location of the oneor more features of the user is outside a predefined location range, orboth the determined angle of the device with respect to the direction ofgravity is outside a predefined angle range and the identified locationof the one or more features of the user is outside a predefined locationrange.

Similarly, the height of the blood pressure sensor may be determined tobe at the heart level of the user where the determined angle of thedevice with respect to the direction of gravity is within a predefinedangle range, the identified location of the one or more features of theuser is within a predefined location range, or both the determined angleof the device with respect to the direction of gravity is within apredefined angle range and the identified location of the one or morefeatures of the user is within a predefined location range.

Thus, in some embodiments, both of the described parameters (namely, theparameters of the determined angle of the device 100 with respect to thedirection of gravity and the identified location of the one or moreanatomical features of the user in the image relative) may be checked.If one or both of these parameters are outside their respectivepredefined ranges, the height of the blood pressure sensor 102 may bedetermined to be different to the heart level of the user (which may,for example, be a height that is inappropriate or less than optimal forblood pressure measurements). On the other hand, if one or both of theseparameters are within their respective predefined ranges, the height ofthe blood pressure sensor 102 may be determined to be at the heart levelof the user (which may, for example, be a height that is appropriate oroptimal for blood pressure measurements).

In embodiments in which the distance of the device 100 with respect tothe body is determined based on the location of the one or morefeatures, the determination of the height of the blood pressure sensor102 relative to the heart level of the user may be further based on thisdetermined distance. In this way, the height of the blood pressuresensor 102 relative to the heart level may be determined more precisely,or an absolute deviation of the height of the blood pressure sensor 102from the heart level (for example, in centimetres) may be determined.

FIG. 3 is an illustration of the device 100 in use by a user 300according to an embodiment. As illustrated in FIG. 3, an angular sensoris used to determine the angle that the device 100 makes relative to thedirection of gravity and a camera is used to identify the location ofone or more features of the user 300 when the user 300 is (at leastpartially) in the field of view 302 of the camera.

In this illustrated example embodiment, an image of the user and apredefined location range 306 is displayed on a display 308 of thedevice 100 comprising the blood pressure sensor 102. However, asdescribed earlier, the image of the user and the predefined locationrange 306 may instead be displayed on a display of a device 100 that isa different device to the device 100 comprising the blood pressuresensor 102 according to other example embodiments. The predefinedlocation range 306 defines a location range on the display 308 of thedevice 100 for the user to align one or more of their features (such asany of those mentioned earlier). In the example embodiment shown in FIG.3, the one or more features of the user are the eyes 304 of the user.Thus, in the example embodiment shown in FIG. 3, the location of theeyes 304 of the user relative to the predefined location range 306 ofthe display 308 of the device 100 are identified (at block 204 of FIG.2). As described above, a height of the blood pressure sensor of thedevice 100 relative to a heart level 310 of the user 300 can bedetermined (at block 206 of FIG. 2) based on the determined angle of thedevice 100 with respect to the direction of gravity and the identifiedlocation of the one or more features of the user 300.

Through the determined height of the blood pressure sensor 102 relativeto the heart level of the user, the combination of the determined angleof the device 100 with respect to the direction of gravity and theidentified location of one or more features of the user holding thedevice 100 (or the combination of an angular sensor and a camera) can beused to control the device 100 to ensure that hydrostatic effects areminimised or eliminated. Thus, returning back to FIG. 2, at block 208,the device 100 is controlled based on the determined height of the bloodpressure sensor 102 relative to the heart level of the user. The device100 can be controlled based on the determined height of the bloodpressure sensor 102 relative to the heart level of the user in a varietyof ways.

In some embodiments, when the height of the blood pressure sensor isdetermined to be at the heart level of the user, the blood pressuresensor 102 of the device 100 may be controlled to acquire a bloodpressure measurement from the user.

In some embodiments, when the height of the blood pressure sensor 102 isdetermined to be different to the heart level of the user, the device100 may be controlled to output to the user one or more of thedetermined angle of the device 100 with respect to the direction ofgravity and the identified location of the one or more features of theuser (such as via a user interface 110, which can be a user interface ofthe device or a user interface external to the device). In someembodiments, the predefined angle range, the predefined location range,or both the predefined angle range and the predefined location range mayalso be output to the user (such as via a user interface 110, which canbe a user interface of the device or a user interface external to thedevice). In this way, information is provided that enables the user toensure that the device 100 is positioned to avoid hydrostatic effectssuch that an accurate blood pressure measurement can be acquired fromthe blood pressure sensor 102.

Alternatively or in addition, in some embodiments, when the height ofthe blood pressure sensor 102 is determined to be different to the heartlevel of the user, the device 100 may be controlled to output to theuser an instruction to adjust any one or more of the angle of the device100 with respect to the direction of gravity, the location (for example,the height) of the one or more features of the user, and the angle ofthe body (or posture) of the user. As mentioned earlier, the angle ofthe body of the user may be inferred from the angle of the device 100with respect to the direction of gravity. The device 100 may becontrolled to output the instruction to the user via a user interface110, which can be a user interface of the device or a user interfaceexternal to the device.

The instruction may be, for example, an instruction to move the device100 in a certain direction, an instruction to tilt the device 100 in acertain direction, an instruction to alter the angle of the body (orposture) of the user, or any combination of these instructions. In someembodiments, an instruction may be output whenever the height of theblood pressure sensor 102 is determined to be different to the heartlevel of the user. For example, in some embodiments, an instruction maybe output whenever the determined angle of the device 100 with respectto the direction of gravity is outside the predefined angle range, theidentified location of the one or more features of the user is outsidethe predefined location range, or both the determined angle of thedevice 100 with respect to the direction of gravity is outside thepredefined angle range and the identified location of the one or morefeatures of the user is outside the predefined location range. In thisway, feedback can be provided to the user to guide the user to positionthe device 100 at (or near or closer to) the heart level of the user atthe appropriate orientation to reduce or eliminate hydrostatic effects.

Alternatively or in addition, in some embodiments, when the height ofthe blood pressure sensor is determined to be different to the heartlevel of the user, the device 100 may be controlled to output to theuser an error notification (such as via a user interface 110, which canbe a user interface of the device or a user interface external to thedevice). The error notification may, for example, indicate that a bloodpressure measurement is false, incorrect, or has not been determined.

In some embodiments, an error notification may be output whenever theheight of the blood pressure sensor 102 is determined to be different tothe heart level of the user. For example, in some embodiments, an errornotification may be output whenever the determined angle of the device100 with respect to the direction of gravity is outside the predefinedangle range, the identified location of the one or more features of theuser is outside the predefined location range, or both the determinedangle of the device 200 with respect to the direction of gravity isoutside the predefined angle range and the identified location of theone or more features of the user is outside the predefined locationrange. In this way, the user can be guided to position the device 100differently until the device 100 is at (or near) the heart level of theuser at the appropriate orientation to reduce or eliminate hydrostaticeffects.

In some embodiments, the error notification may be output where theangle of the device 100 with respect to the direction of gravity is morethan a predefined threshold value. For example, the predefined thresholdvalue may be at or around 90 degrees to prevent blood pressuremeasurements being acquired when the user is laying down (since, asmentioned earlier, the angle of the body of the user may be inferredfrom the angle of the device 100 with respect to the direction ofgravity).

Alternatively or in addition, in some embodiments, when the height ofthe blood pressure sensor 102 is determined to be different to the heartlevel of the user, the blood pressure sensor 102 of the device 100 maybe controlled to acquire a blood pressure measurement from the user. Inthese embodiments, the acquired blood pressure measurement can then beadjusted based on the difference between the height of the bloodpressure sensor and the heart level of the user.

The difference between the height of the blood pressure sensor and theheart level of the user can be determined as an absolute heightdifference. In some embodiments, for example, the difference between theheight of the blood pressure sensor and the heart level of the user maybe determined based on the location of the one or more features of theuser holding the device in relation to a target location for the one ormore features of the user for the blood pressure sensor 102 of thedevice 100 to be positioned at the heart level of the user. The heightdifference may be determined as the number of pixels between theidentified location of the one or more features of the user holding thedevice and the target location for the one or more features. In someembodiments, a scaling factor may be used to relate the number of pixelsto a distance measurement (for example, centimetres) for the heightdifference. For example, where a feature of the user is located sixpixels below the target location for that feature, the height differencemay be determined as six pixels times the scaling factor.

In embodiments where the distance of the device 100 with respect to thebody is determined based on the location of the one or more features,the determined distance may also be used in the determination of theheight difference. For example, the scaling factor can be made dependenton the determined distance of the device 100 with respect to the body.

The error that is made in a blood pressure measurement with hydrostaticeffects is based on the difference between the height of the bloodpressure sensor and the heart level of the user. Thus, adjustment of theacquired blood pressure measurement can comprise determining thehydrostatic offset from the determined difference between the height ofthe blood pressure sensor and the heart level of the user. Then, thedetermined hydrostatic offset can be used to remove hydrostatic effectsfrom the acquired blood pressure measurement. For example, where thedetermined difference between the height of the blood pressure sensorand the heart level of the user indicates that the blood pressure sensoris above the heart level over the user, the determined hydrostaticeffect is removed from the acquired blood pressure measurement by addingthe hydrostatic offset to the acquired blood pressure measurement.Similarly, where the determined difference between the height of theblood pressure sensor and the heart level of the user indicates that theblood pressure sensor is below the heart level over the user, thedetermined hydrostatic effect is removed from the acquired bloodpressure measurement by subtracting the hydrostatic offset to theacquired blood pressure measurement.

The hydrostatic offset in an acquired blood pressure measurement isapproximately 0.75 mmHg per cm of height difference between the heightof the blood pressure sensor and the heart level of the user. Thus, forexample, where the blood pressure sensor 102 is determined to be 10 cmabove the heart level of the user, the acquired blood pressuremeasurement can be adjusted by adding 10*0.75=7.5 mmHg to the acquiredblood pressure measurement. In this way, any hydrostatic effects thatwould otherwise distort the acquired blood pressure measurement can becompensated (or corrected) to thus provide a more accurate bloodpressure measurement.

In any of the embodiments where the blood pressure sensor 102 of thedevice 100 is controlled to acquire a blood pressure measurement fromthe user, the blood pressure measurement may be acquired from the userusing any suitable technique for acquiring a blood pressure measurement.As mentioned earlier, the blood pressure measurement may be acquiredfrom arterial oscillations detected by the blood pressure sensor 102.The arterial oscillations can comprise volumetric oscillations, pressureoscillations, or both volumetric and pressure oscillations. The arterialoscillations can be detected as a function of applied pressure. In theseembodiments, the arterial oscillations versus applied pressure can beprocessed using standard techniques to acquire the blood pressuremeasurement (such as any one or more of a value for the systolic bloodpressure, the diastolic blood pressure, and mean arterial bloodpressure).

In any of the embodiments in which a blood pressure measurement isacquired, the method may further comprise providing (for example,rendering, outputting, or displaying) the acquired blood pressuremeasurement to the user. For example, as mentioned earlier, the controlunit 104 may control a user interface 110 (which may be a user interfaceof the apparatus 100 or a user interface external to the device) toprovide (for example, render, output, or display) to the user theacquired blood pressure measurement.

There is therefore provided an improved device comprising a bloodpressure sensor and an improved method for controlling the device. Asdescribed herein, the device can be controlled in a manner that can helpto reduce, prevent, or eliminate hydrostatic effects in blood pressuremeasurements. In this way, more accurate blood pressure measurements canbe acquired by way of a simple yet effective method.

There is also provided a computer program product comprising a computerreadable medium, the computer readable medium having computer readablecode embodied therein. The computer readable code is configured suchthat, on execution by a suitable computer or processor, the computer orprocessor is caused to perform the method or methods described herein.

Variations to the disclosed embodiments can be understood and effectedby those skilled in the art in practicing the claimed invention, from astudy of the drawings, the disclosure and the appended claims. In theclaims, the word “comprising” does not exclude other elements or steps,and the indefinite article “a” or “an” does not exclude a plurality. Asingle processor or other unit may fulfil the functions of several itemsrecited in the claims. The mere fact that certain measures are recitedin mutually different dependent claims does not indicate that acombination of these measures cannot be used to advantage. A computerprogram may be stored/distributed on a suitable medium, such as anoptical storage medium or a solid-state medium supplied together with oras part of other hardware, but may also be distributed in other forms,such as via the Internet or other wired or wireless telecommunicationsystems. Any reference signs in the claims should not be construed aslimiting the scope.

The invention claimed is:
 1. A method for controlling a devicecomprising a blood pressure sensor comprising: determining an angle ofthe device with respect to the direction of gravity; identifying, in animage of a user, a location of one or more anatomical features of theuser holding the device; determining whether the determined angle iswithin a range of predefined angles; determining whether the determinedlocation is within a range of predefined locations in the image;determining whether the blood pressure sensor is at a heart level of theuser based on the determined angle and the determined location; whereinthe blood pressure sensor is determined to be at the heart levelwhenever the determined angle is within the range of predefined anglesand the identified location is within the range of predefined locations;and controlling the blood pressure sensor to acquire a blood pressuremeasurement from the user when the blood pressure sensor is determinedto be at the heart level of the user.
 2. The method as claimed in claim1, wherein controlling the device comprises: controlling the device tooutput to the user the determined angle of the device with respect tothe direction of gravity and the identified location of the one or moreanatomical features of the user when the blood pressure sensor isdetermined not to be at the heart level of the user.
 3. The method asclaimed in claim 1, wherein controlling the device comprises:controlling the device to output to the user an instruction to adjustthe angle of the device with respect to the direction of gravity and thelocation of the one or more anatomical features of the user when theblood pressure sensor is determined not to be at the heart level of theuser.
 4. The method as claimed in claim 1, wherein controlling thedevice comprises: controlling the device to output to the user an errornotification when the blood pressure sensor is determined not to be atthe heart level of the user.
 5. The method as claimed in claim 1,wherein controlling the device comprises: determining a height of theblood pressure sensor relative to the heart level of the user based onthe identified location of the one or more anatomic features in theimage; controlling the blood pressure sensor to acquire a blood pressuremeasurement from the user when the height of the blood pressure sensoris determined to be different to the heart level of the user; andadjusting the acquired blood pressure measurement based on thedifference between the height of the blood pressure sensor and the heartlevel of the user.
 6. The method as claimed in claim 1, wherein the oneor more anatomical features of the user comprise at least one of: one orboth eyes of the user; the mouth of the user; and the nose of the user.7. A non-transitory computer-readable medium that includes a programthat, when executed by a processor, causes the processor to control adevice comprising a blood pressure sensor by: determining an angle ofthe device with respect to the direction of gravity; identifying, in animage of the user, a location of one or more anatomical features of theuser holding the device; determining whether the angle of the device iswithin a range of predefined angles; determining whether the location ofthe one or more anatomical features is within a range of predefinedlocations in the image; determining whether the blood pressure sensor isat a heart level of the user based on the determined angle and thedetermined location; wherein the blood pressure sensor is determined tobe at a heart level of the user whenever the determined angle is withinthe range of predefined angles and the identified location is within therange of predefined locations; and controlling the blood pressure sensorto acquire a blood pressure measurement from the user when the bloodpressure sensor is determined to be at the heart level of the user. 8.The medium as claimed in claim 7, wherein the program further causes theprocessor to: determine a height of the blood pressure sensor relativeto the heart level of the user based on the identified location of theone or more anatomic features in the image; control the blood pressuresensor to acquire a blood pressure measurement from the user when theheight of the blood pressure sensor is determined to be different to theheart level of the user; and adjust the acquired blood pressuremeasurement based on the difference between the height of the bloodpressure sensor and the heart level of the user.
 9. The medium asclaimed in claim 7, wherein the program further causes the processor toprovide the blood pressure measurement to a display.
 10. The medium asclaimed in claim 7, wherein the program further causes the processor tooutput to the user an error notification when the height of the bloodpressure sensor is determined not to be at the heart level of the user.11. The medium as claimed in claim 7, wherein the one or more anatomicalfeatures of the user comprise at least one of: one or both eyes of theuser; the mouth of the user; and the nose of the user.
 12. A devicecomprising: a blood pressure sensor for acquiring a blood pressuremeasurement from a user holding the device; and a control unitconfigured to: determine an angle of the device with respect to thedirection of gravity; identify, in an image of the user, a location ofone or more anatomical features of the user holding the device;determine whether the angle of the device is within a range ofpredefined angles; determine whether the location of the one or moreanatomical features is within a range of predefined locations in theimage; determine whether the blood pressure sensor is at a heart levelof the user based on the determined angle and the determined location;wherein the blood pressure sensor is determined to be at a heart levelof the user whenever the determined angle is within the range ofpredefined angles and the identified location is within the range ofpredefined locations; and control the blood pressure sensor to acquire ablood pressure measurement from the user when the blood pressure sensoris determined to be at the heart level of the user.
 13. The device asclaimed in claim 12, the device further comprising: an angular sensor,wherein the control unit is configured to control the angular sensor todetermine the angle of the device with respect to the direction ofgravity.
 14. The device as claimed in claim 12, the device furthercomprising: a camera, wherein the control unit is configured to controlthe camera to identify the range of predefined locations in a display ofthe image of the user.
 15. The device as claimed in claim 12, the devicefurther comprising: a user interface, wherein when the blood pressuresensor is determined not to be at the heart level of the user, thecontrol unit is configured to control the user interface to output tothe user any one or more of: the determined angle of the device withrespect to the direction of gravity; the identified location of the oneor more anatomical features of the user; an instruction to adjust atleast one of: the angle of the device with respect to the direction ofgravity, the location of the one or more anatomical features of the userin the image of the user, and an angle of the body of the user; and anerror notification.
 16. The device as claimed in claim 12, wherein theblood pressure sensor comprises at least one of: a volume sensor; and apressure sensor.
 17. The device as claimed in claim 12, wherein thecontrol unit is configured to: determine a height of the blood pressuresensor relative to the heart level of the user based on the identifiedlocation of the one or more anatomic features in the image; control theblood pressure sensor to acquire a blood pressure measurement from theuser when the height of the blood pressure sensor is determined to bedifferent to the heart level of the user; and adjust the acquired bloodpressure measurement based on the difference between the height of theblood pressure sensor and the heart level of the user.
 18. The device asclaimed in claim 12, further comprising a display, wherein the controlunit is configured to provide the blood pressure measurement to thedisplay.
 19. The device as claimed in claim 12, wherein the control unitis configured to output to the user an error notification when theheight of the blood pressure sensor is determined not to be at the heartlevel of the user.
 20. The device as claimed in claim 12, wherein theone or more anatomical features of the user comprise at least one of:one or both eyes of the user; the mouth of the user; and the nose of theuser.